1. Field of the Invention
The present invention relates to a refrigeration cycle for such as an air conditioner.
2. Description of the Related Art
FIG. 26 is a block diagram illustrating a conventional refrigeration cycle for an air conditioner. With referring to the figure, a reference numeral 1 denotes a compressor, which sucks in a low-temperature and low-pressure gas refrigerant in an accumulator 6, compresses the gas refrigerant, and discharges a high-temperature and high-pressure gas refrigerant. A reference numeral 2 denotes a four-way valve. Reference numerals 3a, 3b, 3c denote indoor heat exchangers. Reference numerals 4a, 4b, 4c denote flow regulators. A reference numeral 5 denotes an outdoor heat exchanger. A reference numeral 6 denotes the accumulator.
According to the thus configured conventional refrigeration cycle for an air conditioner, a high-temperature and high-pressure gas refrigerant is discharged from the compressor 1 and then enters the outdoor heat exchanger 5 through the four-way valve 2 in a cooling operation, for example. This gas refrigerant is heat-exchanged with outside air by the outdoor heat exchanger 5 to become a liquefied refrigerant. Then the liquefied refrigerant diverges and depressurized through the flow regulators 4a, 4b, 4c to become a low dried two-phase refrigerant, and enters the respective indoor heat exchangers 3a, 3b, 3c. Then, the two-phase refrigerant is heat-exchanged with room air to evaporate to become a highly dried two-phase refrigerant. This two-phase refrigerant enters the accumulator 6 through the four-way valve 2. The gas refrigerant in the accumulator 6 is sucked in again by the compressor 1, at which time residual refrigerant is reserved in the accumulator 6.
Such a conventional refrigeration cycle as mentioned above is provided with the accumulator 6 for reserving residual refrigerant between the suction inlet side of the compressor 1 and the four-way valve 2. Under the condition that the refrigeration cycle is operating, the temperature of the liquid refrigerant in the accumulator 6 is equivalent to a saturation temperature corresponding to the suction pressure of the compressor 1, which is a low temperature of five degrees centigrade or below in a normal state of use. However, if using such refrigerating machine oil which can be weakly dissolved in a refrigerant as alkyl-benzene oil, for example, in the conventional refrigeration cycle, the saturation solubility of the refrigerating machine oil of a liquid refrigerant in the accumulator at a low temperature becomes a maximum of 0.5% or below. The liquid refrigerant is reserved at a temperature as low as or lower than five degrees centigrade as shown in FIG. 27. Thus, the saturation solubility is lower than 0.8% which is an oil circulation rate in the refrigeration cycle of a general air conditioner. As a result, the refrigerating machine oil is separated in two layers, and the refrigerating machine oil having a smaller specific gravity than that of a liquid refrigerant floats on the surface of the liquid refrigerant. However, according to the conventional refrigeration cycle, the oil return port of the accumulator 6 is provided at a lower level of a pipe in the accumulator. For that reason, the refrigerating machine oil is not allowed to return to the compressor from the accumulator, thereby stagnating in the accumulator. As a result, refrigerating machine oil in the compressor dries up, which may cause a problem of damaging the compressor or the like.
It is an object of the present invention to provide a highly reliable refrigeration cycle having residual refrigerant. According to this refrigeration cycle, it is designed that the refrigerating machine oil does not stagnate in the refrigeration cycle after flowing out from the compressor if the refrigerating machine oil is weakly soluble in a refrigerant. Thus, the compressor may be prevented from the exhaustion of the oil. In addition to that, even if the accumulator is removed from the cycle, a large amount of wet vapor suction into the compressor may also be avoided.
These and other objects of the embodiments of the present invention are accomplished by the present invention as hereinafter described in further detail.
According to one aspect of the present invention, a refrigeration cycle, which connects with a compressor, an outdoor heat exchanger, a flow regulator and an indoor heat exchanger by pipes to form a loop, and contains refrigerating machine oil and a refrigerant, may include a control section. The control section may control a saturation solubility of the refrigerating machine oil of a liquid refrigerant reserved in the refrigeration cycle so that the saturation solubility does not become lower than an oil circulation rate of the refrigerating machine oil in the refrigeration cycle.
The refrigerating machine oil may be weakly soluble in the refrigerant.
The control section may include a receiver and at least one of a first flow regulator and a second flow regulator. The receiver may be placed between the outdoor heat exchanger and the indoor heat exchanger. The receiver may reserve a residual refrigerant. The first flow regulator may be provided between the pipes which are connected, respectively, with the receiver and the outdoor heat exchanger. The second flow regulator may be provided between the pipes which are connected, respectively, with the receiver and the indoor heat exchanger.
The refrigeration cycle may further include an operating time counter for counting an operating period of the compressor. Then, the compressor may be controlled so as to change an operation frequency to a given preset operation frequency and then operate for a given period whenever the operating period of the compressor obtained from the operating time counter exceeds a given preset period.
The refrigeration cycle may further include a start controller for operating the compressor with a given preset operation frequency, which is lower than a normal operation frequency, for a given period when an operation of the refrigeration cycle is started.
The refrigeration cycle may further include a heater for heating the compressor.
In the refrigeration cycle, one of an HRC refrigerant and an HC refrigerant may be used as the refrigerant.
In the refrigeration cycle, alkyl-benzene oil may be used as the refrigerating machine oil.
According to another aspect of the present invention, a method for controlling a refrigeration cycle which connects with a compressor, an outdoor heat exchanger, a flow regulator and an indoor heat exchanger by pipes to form a loop and contains refrigerating machine oil and a refrigerant, may include the step of controlling a saturation solubility of the refrigerating machine oil of a liquid refrigerant reserved in the refrigeration cycle so that the saturation solubility does not become lower than an oil circulation rate of the refrigerating machine oil in the refrigeration cycle.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.